1. Field of the Invention
This invention relates to a muffler for an internal combustion engine such as a small air-cooled two-stroke gasoline engine which is suited for use in a portable power working machine such as a brush cutter or a chain saw.
2. Description of the Related Art
Mufflers are known having a structure where its interior is provided with a large number of pipes and partition walls and, at the same time, a plurality of expansion chambers forming a multistage assembly. For example, Japanese Utility Model Publication H5-44489 describes a muffler having an inlet pipe defining a first chamber which communicates, via an inlet port formed in a main body of the muffler, with the exhaust port of the internal combustion engine, and with a partition plate placed inside the main body to define a second chamber and a third chamber. The first chamber communicates with the second and third chambers via holes differing in area from that of the inlet port at a predetermined ratio. The partition plate has a hole for communicating the second chamber with the third chamber, the area of the hole differing from that of the inlet port at a predetermined ratio. Either the second chamber or the third chamber has an outlet pipe communicating with the external atmosphere outside of the main body. The outlet pipe has a hole opened to the other one of the second chamber and the third chamber and has an area differing from that of the outlet pipe at a predetermined ratio, thus providing the muffler with a large number of pipes and partition walls and with a plurality of expansion chambers which form a multistage assembly.
Further, it is generally known that with a muffler for an internal combustion engine, the muffling effect can be enhanced by increasing the muffler""s capacity (the capacity of the expansion chamber) or by increasing the number of expansion chambers to be formed into a multistage assembly. However, in the case of portable-type working machines in particular, it is impossible to spare so much space for installing the muffler, thus inevitably limiting the muffler""s capacity. On the other hand, any increase in the number of pipes and partition walls would result in a structure of increased complexity as well as in increases of weight and manufacturing cost.
This invention relates to the aforementioned circumstances, and therefore an object of the present invention is to provide a muffler for an internal combustion engine which is capable of effectively enhancing the muffling effect thereof without any substantial increase in size, weight and manufacturing cost.
With a view toward realizing the aforementioned object, a muffler for an internal combustion engine is provided according to this invention in which the exhaust gas ejected from the exhaust port of the internal combustion engine is divided into at least two flows, and the divided exhaust gas flows are subsequently impinged against each other before they are finally discharged from a final exhaust port to the external atmosphere.
According to a preferred embodiment of this invention, the muffler is provided with an expansion chamber into which the exhaust gas is to be introduced from the exhaust port, and the expansion chamber is provided with at least two openings for impingement (hereinafter, referred to as xe2x80x9cimpingement openingsxe2x80x9d), which enable the exhaust gas to be divided into at least two exhaust gas flows which are subsequently impinged against each other.
It is preferred that a collision chamber provided with the aforementioned final exhaust port is provided in a manner to cover the impingement openings.
Preferably, the expansion chamber comprises by a first expansion chamber into which exhaust gas is directly introduced from the exhaust port, and a second expansion chamber which is disposed next to and on the outer peripheral side of the first expansion chamber into which the exhaust gas is directly introduced via a blow-off port from the first expansion chamber. The second expansion chamber is provided with the impingement openings.
The first expansion chamber, the second expansion chamber and the collision chamber are preferably and by way of example defined by a metallic panel.
The aforementioned impingement openings preferably comprise louver-like openings (referred to herein as xe2x80x9clouvered openingsxe2x80x9d) which are symmetrically formed such that the directions of blow-off of the louvered openings are enabled to be intersected with each other.
In a further preferred embodiment of the muffler according to this invention, the collision chamber includes a plurality of final exhaust ports.
The first expansion chamber is formed of a rectangular tube provided with an exhaust gas inlet port wherein one sidewall is located on the side where the collision chamber is disposed and three other sidewalls are provided with the aforementioned blow-off port at a region located close to the aforementioned exhaust gas inlet port.
According to the aforementioned preferred embodiment of the muffler for an internal combustion engine according to the present invention, the exhaust gas that has been spouted from the exhaust port of the internal combustion engine is introduced, via the exhaust gas inlet port, into the first expansion chamber at nearly the acoustic velocity and is permitted to expand and diffuse therein, thereby enabling the exhaust sound to be attenuated. In this case, almost all of the exhaust gas that has been introduced into the first expansion chamber is impinged at first against the bottom of the first expansion chamber located facing the exhaust port and is then reflected therefrom. The reflected exhaust gas is ejected via the blow-off port into the second expansion chamber, thus permitting the reflected exhaust gas to expand and diffuse therein, thereby enabling the exhaust sound to be further attenuated.
The exhaust gas that has been expanded and diffused in the second expansion chamber is ejected, via the impingement openings attached to the second expansion chamber, into the collision chamber. At this point, the exhaust gas is divided into two exhaust gas flows, which are subsequently impinged against each other and then permitted to be discharged from the final exhaust ports attached to the collision chamber, thereby allowing the exhaust gas to be diffused into the external atmosphere.
As explained above, since the exhaust gas ejected out of the exhaust port is divided into at least two gas flows, and at the same time, since these exhaust gas flows are forced to impinge against each other before they are discharged into the external atmosphere from the final exhaust ports, it is possible to significantly attenuate the energy of the exhaust gas flow to be discharged into the external atmosphere. As a result, it is now possible to effectively enhance the muffling effect of the muffler without needing to increase the capacity of the muffler itself.
Furthermore, according to the muffler of the present invention, since the collision chamber functioning also as an expansion chamber is formed by making use of a panel, without employing a large number of pipes and partitioning walls, and at the same time, since the impingement openings and final exhaust ports are formed in this panel defining the expansion chambers, the number of parts can be reduced. Moreover, the structure of the muffler can be simplified, thus resulting in the reduction of weight and manufacturing cost.